This invention relates to a silencing system for exhaust gases from internal combustion engines, comprising an intermediate silencing device, a final silencing device and pipings for connecting the inlet of the intermediate silencing device to the exhaust manifold of an internal combustion engine, and the inlet of the final silencing device to the outlet of the intermediate silencing device.
Silencing systems of this kind find a wide application in motor vehicles, because they are generally more effective and easier to be installed than the single-body silencers; however, the known embodiments of these systems have some disadvantages. First of all, the silencing devices being part of the system are usually formed by envelopes containing absorbing materials which, when traversed by the flow of exhaust gases, give rise to noticeable load losses and hence to a considerable back pressure at the exhaust manifold of the engine, which reduces its efficiency. The silencing devices are often effective in attenuating some frequency fields of the exhaust noise of the engine, while they do not sufficiently attenuate other frequency fields. Moreover, whilst usually the intermediate silencing device easily finds a place in the vehicle structure, the final silencing device gives rise to some problems for its installation, especially in small vehicles, owing to the dimensions it should have for being effective. Finally, in the usual embodiments the silencing devices exert no purifying action on the exhaust gases, which are diffused in the ambient more or less silenced but with their full content of contaminant substances, especially carbon monoxyde, sulphur and nitrogen oxides, unburnt hydrocarbons and powdery solid residues.